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SPPU Electrical Engineering (Semester 8)
Power Electronics Controlled Drives
December 2016
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Solve any one question fromQ.1(a,b,) and Q.2(a,b)
1(a) What are the main factors which decide the choice of electrical drive for a given application?
6 M
1(b) A drive has the following parameters:
T = 150-0.1 N, N-m, where N is the speed in rpm.
Initially the drive is operating in steady-state.
The characteristics of the load torque are changed to TL= -100 N-m.
Calculate initial and final equilibrium speeds.
4 M

2(a) Explain the working of single phase Fully controlled rectifier fed separately excited dc motor with armature voltage control, with neat circuit diagram. In which quadrants the motor can be operated assuming rated flux?
6 M
2(b) Draw speed torque characteristics and explain Regenerative bracking in Induction motor.
4 M

Solve any one question fromQ.3 and Q.4(a,b)
3 A 220V, 20 k W dc shunt motor running at rated speed of 1200 rpm is braked using rheostatic braking. The armature resistance is 0.1ohm and motor efficiency 88%. Calculate resistance required to be added in armature circuit to limit braking current to twice the rated value. Also calculate initial braking torque.
10 M

4(a) A star connected squirrel cage induction motor has following ratings ana paramters: 400V, 50 Hz, 4 pole 1370 rpm, Rs = 2 Ω, Rr' = 3Ω Xs=Xr'=3.5 Ω For regenerative braking Assuming motor speed torque characteristics form full load motoring to full load braking to be parallel striaght lines, calculate Speed for a frequency of 30 Hz and 80% of full load torque.
5 M
4(b) With a neat diagram, explain V/f control of 3 phase induction motor. What is the range of speed control?
5 M

Solve any one question fromQ.5(a,b) and Q.6(a,b)
5(a) How speed control is achieved using Vector control of induction motor? Draw vector diagram and explain.
10 M
5(b) Compare and comment on relative merits and demerits VSI and CSI for induction motor drives.
6 M

6(a) Explain the Principle of vector control.
8 M
6(b) Write in brief about topology, control and applications of AC Servo Drives.
8 M

Solve any one question fromQ.7(a,b) and Q.8(a,b)
7(a) Draw neat and diagram to explain vector control of PM Synchronous Motor (PMSM).
8 M
7(b) Explain variable DC link converter topology for PM BLDC Half wave drives for motoring and Regenertive operating modes.
8 M

8(a) What are the Control Strategies used for Permanent Magnet Brushless DC Motor? How constant torque angle control is used?
8 M
8(b) Comment on use Sensorless control of PM BLDC drives.
8 M

Solve any one question Q.9 and Q.10
Solve any 3 question Q.9(a,b,c,d)
9(a) What is the selection criterion for motors? How rating of a motor subjected to variable load duty is decided?
6 M
9(b) What are the requirements of drive for rolling mill operaions?
6 M
9(c) Why controlled torque starting is necessary in Textile machinery drives? How is it achieved?
6 M
9(d) What are the requirements of drive in sugar mills? Explain duty cycle of sugar cetrifuge.
6 M

Solve any 3 question Q.10(a,b,c,d)
10(a) What are various motor duty patterns? How are motors classified based on duty?
6 M
10(b) What motors are suitable for Sugar mill drive applications?
6 M
10(c) How motor duty and heating and cooling cycle affects the temperature of motor?
6 M
10(d) Why 4 quadrant operation of drive is needed for rolling mill drive?
6 M

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